Mark Scheme

Section A: 1. C; 2. B; 3. B; 4. B; 5. B; 6. B. (6)

7 (a) exothermic (1). (b) good insulator (1); reduces heat loss for an accurate temperature change (1). (c) measure a fixed volume of acid and its start temperature (1); add measured volumes of alkali, stir (1); record the highest temperature / temperature change (1). (6)

8 (a) cathode: lead (1); anode: bromine (1). (b) the ions must be free to move (1) to carry charge to the electrodes (1). (c) copper (1); because copper is less reactive than hydrogen (1). (6)

9 (a) hydrogen (1). (b) add excess copper oxide to warm acid (1); filter off excess (1); evaporate to crystallisation point (1); leave to crystallise and dry (1). (5)

10 (a) place a flask over a cross (1); add reactants and time how long until the cross disappears (1); shorter time = faster rate (1). (b) more particles per volume (1); more frequent successful collisions per second (1). (5)

11 (a) acceleration (1). (b) distance travelled (1). (c) Eₖ = ½ × 1000 × 20² = ½ × 1000 × 400 = 200 000 J (1 method, 1 answer). (4)

12 (a) a.c. produces a continually changing magnetic field (1); needed to induce a p.d. in the secondary coil (1). (b) Vp/Vs = Np/Ns → 230/Vs = 200/50 (1); Vs = 230 × (50/200) (1) = 57.5 V (1). (5)

13 (a) advantage: renewable / no CO₂ when running (1); disadvantage: unreliable (depends on wind) / visual impact (1). (b) it is dissipated to the surroundings, usually as thermal energy (1). (c) high voltage means lower current (1); so less energy is wasted as heat in the cables (1). (5)

14 (a) atomic number = number of protons (1); mass number = number of protons + neutrons (1). (b) they have the same number of electrons in their outer shell (1); which determines chemical behaviour (1). (c) reactivity increases down the group (1); the outer electron is further from the nucleus / more shielded (1); so it is lost more easily (1). (d) 12 + (2×16) = 44 (1). (8)

15 (a) sodium loses one electron to form Na⁺ (1); chlorine gains one electron to form Cl⁻ (1). (b) weak intermolecular forces between molecules (1); little energy needed to overcome them (1). (c) total mass of reactants = total mass of products (1). (d) 20 ÷ 0.5 = 40 g/dm³ (1 method, 1 answer). (e) bubble through limewater (1); it turns cloudy/milky (1) — (accept as the single mark). (8)

16 (a) Q = I × t (1). (b) Q = 3 × 20 = 60 C (1 method, 1 answer). (c) R = V ÷ I = 6 ÷ 0.5 = 12 Ω (1 method, 1 answer). (d) the total resistance increases (1). (e) the potential difference is the same across each branch (1); the current is shared between the branches (1). (8)

17 — Levels (6): Indicative: ionic compound = giant lattice of oppositely charged ions held by strong electrostatic forces; conducts only when molten/dissolved (ions free to move). Metal = giant lattice of positive ions in a sea of delocalised electrons; conducts in the solid state because the delocalised electrons are free to move and carry charge.

• L3 (5–6): Both structures described and conductivity correctly explained for each.
• L2 (3–4): Some structure/conductivity detail.
• L1 (1–2): Simple statements.

18 — Levels (6): Indicative: reactions need collisions with at least the activation energy. Higher temperature → particles move faster, collide more often, and more collisions have enough energy → faster rate. Larger surface area (smaller pieces) → more particles exposed → more frequent collisions → faster. Rate can be measured by collecting the gas in a gas syringe (or measuring mass loss on a balance) at regular time intervals and plotting volume against time.

• L3 (5–6): Both factors explained by collision theory and a valid method to measure rate.
• L2 (3–4): Some of the factors and/or the method.
• L1 (1–2): Simple statements.

19 — Levels (6): Indicative: in an exothermic reaction energy is transferred to the surroundings (temperature rises); the products are at a lower energy than the reactants, so the reaction profile goes down. In an endothermic reaction energy is taken in from the surroundings (temperature falls); the products are higher in energy, so the profile goes up. Breaking bonds is endothermic and making bonds is exothermic; the overall change depends on the balance between the two.

• L3 (5–6): Both types explained with energy transfer, bond breaking/making and profile shape.
• L2 (3–4): Some correct points for both or detail for one.
• L1 (1–2): Simple statements.

20 — Levels (6): Indicative: a current-carrying wire in a magnetic field experiences a force because the wire's field interacts with the magnet's field. The force is greatest when the wire is at 90° to the field and zero when parallel. Reversing the current or the field reverses the direction (Fleming's left-hand rule). The size increases with a larger current or stronger field (F = BIL). Used in electric motors / loudspeakers.

• L3 (5–6): Explains the effect, how size and direction change, and names a device.
• L2 (3–4): Some explanation with one or two factors.
• L1 (1–2): Simple statements.

21 — Levels (6): Indicative: a step-up transformer increases the voltage for transmission; for a fixed power, higher voltage means a lower current (P = VI); energy lost as heat in the cables depends on current², so a lower current greatly reduces wasted energy. Step-down transformers then reduce the voltage to a safe value for use. Transformers only work with alternating current.

• L3 (5–6): Links high voltage → low current → less heat loss with the correct roles of both transformers.
• L2 (3–4): Some of the chain or roles.
• L1 (1–2): Simple statements.

22 — Levels (4): Indicative: reactivity decreases down Group 7 because the outer shell is further from the nucleus and more shielded, so it is harder to gain an electron. A more reactive halogen displaces a less reactive one from a solution of its salt, e.g. chlorine + potassium bromide → potassium chloride + bromine.

• L2 (3–4): Correct trend with explanation and a valid displacement example.
• L1 (1–2): Simple statements.

Sample Answers with Examiner Commentary

Question 17 — Sample Answers

Grade 9 answer "An ionic compound is a giant lattice of positive and negative ions held together by strong electrostatic forces acting in all directions. It only conducts electricity when molten or dissolved, because then the ions are free to move and carry charge; when solid the ions are fixed in place. A metal is a giant lattice of positive metal ions surrounded by a 'sea' of delocalised electrons. It conducts electricity even when solid because these delocalised electrons are free to move through the structure and carry the charge." Mark: 6/6. Examiner commentary: Both structures are described accurately and the conductivity of each is explained with the correct reason (free-moving ions vs delocalised electrons), including why ionic solids do not conduct. Top band.

Grade 6 answer "Ionic compounds are made of ions and only conduct when melted or dissolved because the ions can move. Metals have delocalised electrons that move and carry charge so they conduct." Mark: 4/6. Examiner commentary: Correct on both conductivity explanations, but the structures (giant ionic lattice; metal ions in a sea of electrons) are not described, and it does not say why ionic solids fail to conduct. Adding those reaches the top band.

Question 12(b) — Sample Answers

Grade 9 answer "Vp/Vs = Np/Ns, so 230/Vs = 200/50. Rearranging gives Vs = 230 × (50/200) = 230 × 0.25 = 57.5 V." Mark: 3/3. Examiner commentary: Correct equation, substitution and answer — recognised as a step-down transformer.

Grade 6 answer "It steps down so the voltage is lower. 230 ÷ 4 = 57.5 V." Mark: 2/3. Examiner commentary: Correct answer and recognition of step-down, but the transformer equation/ratio is not shown, losing the method mark.